Mid-turbine frame buffer system

ABSTRACT

A mid-turbine frame buffer system for a gas turbine engine includes a mid-turbine frame that supports a shaft by a bearing. An air compartment and a bearing compartment are arranged radially inward of the mid-turbine frame. The bearing compartment is arranged within the air compartment and includes first and second contact seals arranged on either side of the bearing. The air compartment includes multiple air seals. A high pressure compressor is fluidly connected to the air compartment and is configured to provide high pressure air to the air compartment. A method of providing pressurized air to a buffer system includes sealing a bearing compartment with contact seals, surrounding the bearing compartment with an air compartment, and supplying high pressure air to the air compartment.

BACKGROUND

This disclosure relates to a mid-turbine frame buffer system for a gasturbine engine.

A mid-turbine frame is a structural case that is used to support the aftend of the high spool shaft of a turbofan engine. The mid-turbine frameis located between the high pressure turbine and low pressure turbine, alocation where the core flowpath pressure and temperature are high. Thestatic mid-turbine frame supports a rotating high speed shaft through abearing enclosed in a buffered bearing compartment. Since the bearingmust be cooled and lubricated with a constant oil flow, seals are usedto contain the oil at static-to-rotating interfaces. The buffer airpressure outside of the bearing compartment must remain higher than thepressure inside the compartment so that air always leaks into thecompartment, not out, so that the oil is contained within the bearingcompartment.

SUMMARY

A mid-turbine frame buffer system for a gas turbine engine includes amid-turbine frame that supports a shaft by a bearing. An air compartmentand a bearing compartment are arranged radially inward of themid-turbine frame. The bearing compartment is arranged within the aircompartment and includes a seal assembly provided adjacent the bearing.The air compartment includes two or more air seals. An air source isfluidly connected to the air compartment and is configured to providepressurized air to the air compartment.

In a further embodiment of the above, the bearing may be a rollerbearing.

In a further embodiment of any of the above, the mid-turbine frame maybe arranged axially between the high and low pressure turbines.

In a further embodiment of any of the above, the air source may be ahigh pressure compressor. Further, the high pressure compressor and thehigh pressure turbine may be supported on the shaft.

In a further embodiment of any of the above, a lubrication pump may befluidly connected to the bearing compartment by a scavenge line.

In a further embodiment of any of the above, the seal assembly mayinclude first and second contact seals. Further, each of the first andsecond contact seals may have first and second members in engagementwith one another. At least one of the first and second members may beconstructed from a carbon material.

In a further embodiment of any of the above, the air seals may include alabyrinth seal.

In a further embodiment of any of the above, the air seals may include abrush seal.

In a further embodiment of any of the above, the mid-turbine frame mayinclude a member arranged in a core flow path. The member may provide apassage fluidly connecting mid-turbine frame outer and inner areas toone another for delivering the pressurized air to the air compartment.

A method of providing pressurized air to a buffer system includessealing a bearing compartment with two or more seals, surrounding thebearing compartment with an air compartment, and supplying pressurizedair to the air compartment.

In a further embodiment of the above, the two or more seals may becontact seals that may include a carbon material.

In a further embodiment of any of the above, the two or more seals mayinclude contact seals and two or more air seals. Further, at least oneof the two or more air seals may be at least one of a labyrinth seal anda brush seal.

In a further embodiment of any of the above, the pressurized air mayinclude high pressure compressor air.

In a further embodiment of any of the above, the bearing compartment maybe provided between low and high pressure turbines.

Another embodiment address a gas turbine engine that includes, amongother possible things, a fan; a compressor section fluidly connected tothe fan; a combustor fluidly connected to the compressor section; aturbine section fluidly connected to the combustor, the turbine sectionincluding a high pressure turbine coupled to the high pressurecompressor via a shaft; a low pressure turbine; and a mid-turbine framepositioned between the high pressure turbine and the low pressureturbine, the mid-turbine frame supporting the shaft by a bearing; and amid-turbine frame buffer system that includes an air compartment; and abearing compartment arranged radially inward of the mid-turbine frame,the bearing compartment arranged within the air compartment, the bearingcompartment including a seal assembly provided adjacent the bearing, theair compartment including two or more air seals. The compressor isfluidly connected to the air compartment and is configured to providepressurized air to the air compartment.

In a further embodiment of the foregoing as turbine engine, the bearingmay be a roller bearing.

In another further embodiment of any of the foregoing gas turbine engineembodiments, the engine may further include a lubrication pump fluidlyconnected to the bearing compartment by a scavenge line.

In another further embodiment of any of the foregoing gas turbine engineembodiments, the seal assembly may include first and second contactseals. Further, each of the first and second contact seals may havefirst and second members in engagement with one another. In addition, atleast one of the first and second members may be constructed from acarbon material.

In another further embodiment of any of the foregoing gas turbine engineembodiments, the air seals may include at least one of a labyrinth sealand a brush seal.

In another further embodiment of any of the foregoing gas turbine engineembodiments, the gas turbine engine may be a high bypass geared aircraftengine having a bypass ratio of greater than about six (6).

In another further embodiment of any of the foregoing gas turbine engineembodiments, the gas turbine engine may include a low Fan Pressure Ratioof less than about 1.45.

In another further embodiment of any of the foregoing gas turbine engineembodiments, the low pressure turbine may have a pressure ratio that isgreater than about 5.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 schematically illustrates a gas turbine engine.

FIG. 2 schematically depicts a mid-turbine frame buffer system for thegas turbine engine illustrated in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath B whilethe compressor section 24 drives air along a core flowpath C forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 to drive the fan 42 at a lower speed than the lowspeed spool 30. The high speed spool 32 includes an outer shaft 50 thatinterconnects a high pressure compressor 52 and high pressure turbine54. A combustor 56 is arranged between the high pressure compressor 52and the high pressure turbine 54. A mid-turbine frame 57 of the enginestatic structure 36 is arranged generally between the high pressureturbine 54 and the low pressure turbine 46. The mid-turbine frame 57supports one or more bearing systems 38 in the turbine section 28. Theinner shaft 40 and the outer shaft 50 are concentric and rotate viabearing systems 38 about the engine central longitudinal axis A which iscollinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion.

The engine 20 in one example a high-bypass geared aircraft engine. In afurther example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.3 and the low pressure turbine 46 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 20 bypassratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout 5:1. Low pressure turbine 46 pressure ratio is pressure measuredprior to inlet of low pressure turbine 46 as related to the pressure atthe outlet of the low pressure turbine 46 prior to an exhaust nozzle.The geared architecture 48 may be an epicycle gear train, such as aplanetary gear system or other gear system, with a gear reduction ratioof greater than about 2.5:1. It should be understood, however, that theabove parameters are only exemplary of one embodiment of a gearedarchitecture engine and that the present invention is applicable toother gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as bucket cruiseThrust Specific Fuel Consumption (“TSFC”). TSFC is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tambient degR)/518.7)^0.5]. The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

A buffer system 58 is schematically illustrated in FIG. 2. A bearing 60is structurally supported by the mid-turbine frame 57 and supports theouter shaft 50 for rotation. The bearing may be, for example, a rollerbearing a ball bearing or other type of bearing. The bearing 60 isarranged within a bearing compartment 62, which provides an enclosurefor retaining lubrication for the bearing. This enclosure is provided,for example, by walls 64 that support first and second contact seals 66,68 arranged on either side of the bearing 60. Each of the first andsecond contact seals 66, 68 includes first and second members 70, 72that are in engagement with one another such that no gaps are providedbetween the first and second members 70, 72. At least one of the firstand second members 70, 72 is constructed from a carbon material. The useof high pressure ratio face carbon seals reduces airflow into the oilcompartment (as compared to conventional buffer systems), therebyeliminating the need for a conventional breather air tube.

A lubrication pump 88 is fluidly connected to the bearing compartment 62by a scavenge line 90. Any air entering the bearing compartment 62 isexhausted through a vent 92. The lubrication pump 88 has sufficientcapacity to evacuate any small amount of leakage past the first andsecond contact seals 66, 68 into the bearing compartment 62.

The bearing compartment 62 is enclosed within an air compartment 74. Apressurized air source 75 is fluidly coupled to the air compartment 74.“Pressurized” air is air that is provided by, e.g., the high pressurecompressor 52. The mid-turbine frame 57 includes outer and inner areas98, 100 arranged on opposing sides of the mid-turbine frame 57. Apassage 102 fluidly interconnects the inner and outer areas 98, 100 toone another. In one example, the passage 102 is provided by themid-turbine frame airfoil 59.

The air compartment 74 is provided, for example, by walls 82 thatsupport first, second and third air seals 76, 78, 80. The first, secondand third air seals 76, 78, 80 respectively cooperate with first, secondand third surfaces 77, 79, 81. The first surface 77 is provided by ahigh pressure rotor 86. The second surface 79 is provided by the outershaft 50. The third surface 81 is provided by a low pressure rotor 84.The air seals are provided, for example, by one or morelabyrinth/knife-edge seals and/or brush seals. In the exampleillustrated in FIG. 2, the first seal 76 is a labyrinth seal, and thesecond and third air seals 78, 80 are brush seals. Air seals typicallyare not air tight in that they may provide small gaps. Air seals aretypically designed to inhibit leakage by creating a tortuous paththrough which the air must pass. Any air leakage past the first, secondand third air seals 76, 78, 80 vents to the low and high pressureturbines 46, 54, as depicted by the arrows in FIG. 2, which providemultiple air sinks.

In light of the foregoing design, the high pressure buffer systemsurrounding the bearing compartment 62 can vent directly into the turbomachinery primary core flowpath C at the mid turbine frame 57. Since thebuffer air can vent directly into the core flowpath C, the number anddiameter of the high pressure ratio air seals is reduced as compared toconventional turbine engines and, therefore, far less buffer airflowbypassing the turbo machinery is required. The energy in the buffer airentering the core flowpath C is captured in the downstream turbomachinery, thereby improving engine performance. In contrast, inconventional engines, the low buffer pressure systems therein must venta larger mass flow of buffer air to a lower pressure sink in the coreflowpath C downstream from turbo machinery, thereby losing theassociated energy of this air and, correspondingly, negatively impactingengine efficiency.

A turbine engine case 94 supports another bearing 96, which rotationallysupports the inner shaft 40 at a location aft of the bearing 60.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

1. A mid-turbine frame buffer system for a gas turbine enginecomprising: a mid-turbine frame supporting a shaft by a bearing; an aircompartment and a bearing compartment arranged radially inward of themid-turbine frame, the bearing compartment arranged within the aircompartment, the bearing compartment including a seal assembly providedadjacent the bearing and separating the bearing compartment front theair compartment, the air compartment including two or more air seals; anair source fluidly connected to the air compartment and configured toprovide pressurized air to the seal assembly in the air compartment tobuffer the bearing compartment; and wherein the mid-turbine frameincludes a member arranged in a core flow path, the member providing apassage fluidly connecting mid-turbine frame outer and inner areas toone another for delivering the pressurized air to the air compartment.2. The buffer system according to claim 1, wherein the bearing is aroller bearing.
 3. The buffer system according to claim 1, comprisinghigh and low pressure turbines, the mid-turbine frame arranged axiallybetween the high and low pressure turbines.
 4. The buffer systemaccording to claim 3, wherein the air source is a high pressurecompressor, and wherein the high pressure compressor and the highpressure turbine are supported on the shaft.
 5. The buffer systemaccording to claim 1, comprising a lubrication pump fluidly connected tothe bearing compartment by a scavenge line.
 6. The buffer systemaccording to claim 1, wherein the seal assembly comprises first andsecond contact seals, wherein each of the first and second contact sealshas first and second members in engagement with one another, and whereinat least one of the first and second members is constructed from acarbon material.
 7. The buffer system according to claim 1, wherein theair seals includes a labyrinth seal.
 8. The buffer system according toclaim 1, wherein the air seals includes a brush seal.
 9. A gas turbineengine comprising: a fan; a compressor section fluidly connected to thefan; a combustor fluidly connected to the compressor section; a turbinesection fluidly connected to the combustor, the turbine sectioncomprising: a high pressure turbine coupled to the high pressurecompressor via a shaft; a low pressure turbine; and a mid-turbine framepositioned between the high pressure turbine and the low pressureturbine, the mid-turbine frame supporting the shaft by a bearing; and amid-turbine frame buffer system comprising: an air compartment; and abearing compartment arranged radially inward of the mid-turbine frame,the bearing compartment arranged within the air compartment, the bearingcompartment including a seal assembly provided adjacent the bearing andseparating the bearing compartment from the air compartment, the aircompartment including two or more air seals; wherein the compressor isfluidly connected to the air compartment and is configured to providepressurized air to the seal assembly in the air compartment to bufferthe bearing compartment; and wherein the mid-turbine frame includes amember arranged in a core flow path, the member providing a passagefluidly connecting mid-turbine frame outer and inner areas to oneanother for delivering the pressurized air to the air compartment. 10.The gas turbine engine according to claim 9, wherein the bearing is aroller bearing.
 11. The gas turbine engine according to claim 9,comprising a lubrication pump fluidly connected to the bearingcompartment by a scavenge line.
 12. The gas turbine engine according toclaim 9, wherein the seal assembly comprises first and second contactseals, wherein each of the first and second contact seals has first andsecond members in engagement with one another, and wherein at least oneof the first and second members is constructed from a carbon material.13. The gas turbine engine according to claim 9, wherein the air sealsincludes at least one of a labyrinth seal and a brush seal.
 14. The gasturbine engine according to claim 9, wherein the gas turbine engine is ahigh bypass geared aircraft engine having a bypass ratio of greater thanabout six (6).
 15. The gas turbine engine according to claim 9, whereinthe gas turbine engine includes a low Fan Pressure Ratio of less thanabout 1.45.
 16. The gas turbine engine according to claim 9, wherein thelow pressure turbine has a pressure ratio that is greater than about 5.